Studien über die naphthoresorcin-reaktion von tollens : Zur bestimmung von freier uronsaure neben uronosiden,polyuronosiden und neben anderen kohlenhydraten

A micro determination for free uronic acids based on Tollens' reaction is proposed. Sources of error in earlier methods are avoided by the use of phosphoric acid, a reagent solution in glacial acetic acid, and extraction of the dye with toluene. Free glucuronic acid can be determined in presence of glucuronosides of the phenol-ether type up to molar ratios of ca. 1 : 5. Reliable results can also be obtained in the presence of other carbohydrates.     

Lateral growth rates in laser CVD of microstructures

Lateral growth rates of Ni spots deposited on absorbing substrates by decomposition of Ni(CO)₄ with visible Kr⁺ laser light have been measured. The experimental data are consistent with the calculated temperature distributions. The mechanism of decomposition is thermal with an apparent chemical activation energy of 22±3 kcal/mole for the temperature range 350 KT500 K.     

Application of Discrete Wavelet Transform in the Analysis of Nonlinear Chemical System

Oscillations of species concentration are phenomena accompanying several types of electrochemical and purely chemical processes. Importance of analyzing of such processes results from both scientific and practical reasons. In the paper the authors deal with investigation of time dependent spectra of various stages of Belousov-Zhabotinsky type chemical oscillations. As the analytical tool the discrete wavelet transform is proposed.     

Preparative uv-laser photochemistry of the azoalkane spiro(2,3-diazabicyclo [2.2.1]hept-2-ene-7′,1-cyclopropane): Trapping of the 1,4-Diradical 2-(3-Cyclopentenyl) ethyl by Molecular Oxygen

Photo-extrusion of nitrogen from the azoalkane 1 in the presence of molecular oxygen gave besides the hydrocarbons 3 and 5, the endoperoxide 10 and hydroperoxide 11, the former via trapping of the 1,4-diradical 4 by triplet oxygen, the latter by ene-reaction-6f hydrocarbon 5 with singlet oxygen.     

Synthesis of [(MeCyt)2H]I-structure and stability of a dimeric threefold hydrogen-bonded 1-methylcytosinium 1-methylcytosine cation

Reaction of trimethylsilyl-protected cytosine with methyl iodide afforded N1-methylated product. Subsequent treatment with ethanol resulted in cleavage of the protection group forming [(MeCyt)2H]I (4). Identity of was confirmed by microanalysis, mass spectrometry, 1H and 13C NMR spectroscopy and by single-crystal X-ray diffraction analysis. Crystals of consist of dimeric [(MeCyt)2H]+ cations and I- anions. These ions are arranged in the crystal such that there is a strong base stacking (mean stacking distance 3,467 angstroms) and, furthermore, pi interactions between I- and cytosine rings (mean distance 3,737 angstroms). The dimeric [(MeCyt)2H]+ cations are centrosymmetric having three strong hydrogen bonds, namely two terminal N4-H...O' ones (N4...O' 2.815(4) angstroms) and a central N3-H...N3' (N3...N3' 2.813(4) angstroms) one. Quantum chemical calculations on the DFT level of theory show that the gas phase structure of the dimeric cation exhibits two different terminal N-HO hydrogen bonds, a stronger (N4...O' 2.722 angstroms) and a weaker one (N4'...O 2.960 angstroms). The central N3-HN3[prime or minute] hydrogen bond (N3...N3' 2.852 angstroms) was characterized to have an unsymmetrically located proton and a typical double minimum potential with a very low activation barrier. The interaction energy between [(MeCyt)H]+ and MeCyt yielding [(MeCyt)2H]+ was calculated to be -42.4 kcal mol(-1)(ZPE and BSSE corrected). Comparison with the interaction energy (calculated on the same level of the theory) between cytosine and guanine yielding the triply hydrogen-bonded Watson-Crick dimer (-24.2 kcal mol(-1)) revealed a much higher stability of the hydrogen bonds in [(MeCyt)2H]+.     

Stereochemical memory versus Curtin-Hammett behavior in the rearrangement of 1,3-cyclopentanediyl radical cations derived from housanes through structural effects on conformational control

The electron-transfer-catalyzed rearrangement of the housanes 1 affords regioselectively the two cyclopentenes 2 and 3 by 1,2-migration of a group at the methano bridge. Appropriate ring annelation in the intermediary cyclopentane-1,3-diyl radical cation 1(*+) changes the stereochemical course of the rearrangement from complete stereoselectivity (stereochemical memory) for the structurally simple housane 1b to partial loss of stereoselectivity through competing conformational interconversion for the tricyclic housane 1c. Additional cyclohexane annelation, as in the tetracyclic housane 1a, results in complete loss of stereocontrol through Curtin-Hammett behavior, as substantiated by the viscosity dependence on the product ratio of the rearrangement. Whereas in the radical cations 1b(*+) and 1c(*+) the 1,2-shifts (k(2) and k(3)) are faster than the conformational anti <==> syn change (k(1), k(-1)), the reverse applies for the radical cation 1a(*+). Such structural manipulation of conformational effects in radical cation rearrangements has hitherto not been documented.     

Dynamics of theD-dimensional FRW-cosmological models within the superstring-generated gravity model

We study the dynamics of the generalizedD-dimensional (D = 1+3+d) Friedman-Robertson-Walker (FRW) cosmological models in the framework of an extended gravity theory obtained by adding the Gauss-Bonnet term to the standard Einstein-Hilbert action. In our discussion we extensively use methods of dynamical systems. We consider models filled in with a perfect fluid obeying the equation of statep=(–1) and vacuum but non-flat models. We present a detailed analysis of the ten dimensional model and in particular we study the vacuum case. Several phase portraits show how the evolution of this model depends on the parameter.     

Iodine photodissociation laser system Perun II

A construction and exploitation of a medium size iodine photodissociation laser system Perun II is reported. This laser produced pulses of infrared light (=1.315m) up to 50 J in energy and 300 ps in duration. The diameter of the beam is 82 mm. The beam divergence is about 4×10^–4 rad. The laser beam can be focused in a focal spot of a power density exceeding 10¹⁴ W/cm². The resuls of measurements of basic plasma parameters on an Al foil target are also presented. A recent improvement of the system includes a conversion to the second harmonic by a DKDP crystal.Presented at bilateral international seminar of High Temperature Laser Plasma and High Gain Iodine Lasers held on 4 July 1991 in the Inst. of Physics, Czechosl. Acad. Sci., in Prague (organized by Division of Optics of the Inst. of Physics, Czechosl. Acad. Sci., and Physical Section (Plasma Division) of the Union of Czech Mathematicians and Physicists.